The present application relates to a technical field of a lens driver and an image pickup apparatus. In particular, the present application relates to a technical field in which a polymer actuator is arranged outside an outer peripheral surface of a lens unit, which is moved in an optical-axis direction, to decrease the size of the lens unit in a direction orthogonal to the optical-axis direction.
Image pickup apparatuses, such as a video camera and a still camera, each include a lens unit having an image-capturing function. In recent years, a lens unit is included in various electronic devices, such as a mobile phone, a personal computer, and a personal digital assistant (PDA), as the purposes of use of these devices are widened. Therefore, the electronic devices, such as the mobile phone, the personal computer, and the PDA, are used as image pickup apparatuses for capturing images.
An example of such an image pickup apparatus includes a lens unit as a movable part of a lens driver. The lens unit is moved in an optical-axis direction by a polymer actuator for focusing and zooming (for example, see Japanese Unexamined Patent Application Publication No. 2006-293007).
Two types of polymer actuators exist, the two types including an ion conducting actuator and a conductive polymer actuator. The polymer actuators are driving devices whose polymers containing ions are greatly expanded or contracted by applying a voltage of about 2V to the polymer actuators. A polymer actuator includes an ion-exchange resin film (main body) and electrodes bonded to surfaces of the film such that the electrodes are insulated from each other. By applying a potential difference to the electrodes while the ion-exchange resin film is hydrated, the ion-exchange resin film is deformed.
The deformation appears in a transverse direction (bending) and in a longitudinal direction (expanding and contracting). The deformation direction can be designed by changing the structure of the ion-exchange resin film.